Stainless Steel Spiral Coil Tube (Coil Tube) — Vertical Film Condensation Heat Transfer Grade
1. Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coil Tube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 866) is a precision-engineered tubular component formed by winding seamless or welded stainless steel pipe into a continuous helical spiral geometry. This product is specifically designed and optimized for vertical spiral coil tube external film condensation heat transfer applications, where high-efficiency condensation of vapor on the outer surface of the coiled tube is required under natural or forced convection conditions.
Unlike conventional straight-tube heat exchangers, the spiral coil geometry provides a significantly increased surface-area-to-volume ratio, enhanced turbulence at the tube surface, and superior condensate drainage characteristics. The coil tube design enables compact thermal systems with high heat transfer coefficients, making it indispensable in cryogenic processing, refrigeration systems, chemical processing, and power generation industries.
Unique Selling Point: The vertical orientation combined with the spiral coil geometry promotes a thin, uniform condensate film that re-enters the coil on subsequent turns, creating a self-replenishing condensation cycle. This mechanism yields heat transfer coefficients up to 30%–50% higher than equivalent straight-tube configurations under identical operating conditions, as validated by rigorous theoretical modeling and experimental research.
2. Material & Properties
2.1 Base Materials
The Coil Tube is fabricated from austenitic stainless steel grades selected for their exceptional corrosion resistance, thermal stability, and mechanical integrity under condensation environments:
- AISI 304 / SUS304 (UNS S30400) — General-purpose corrosion resistance with excellent formability
- AISI 316L / SUS316L (UNS S31603) — Enhanced chloride resistance with low carbon content for weld integrity
- AISI 321 / SUS321 (UNS S32100) — Titanium-stabilized grade for elevated temperature service
- AISI 316Ti / SUS316Ti (UNS S31635) — Titanium-stabilized with molybdenum for aggressive chemical environments
- AISI 310S / SUS310S (UNS S31008) — High-temperature oxidation resistance for extreme service conditions
2.2 Key Material Properties
| Property | AISi 304 | AISi 316L | AISi 321 | Unit |
|---|---|---|---|---|
| Chemical Composition (Cr) | 18.0–20.0 | 16.0–18.0 | 17.0–19.0 | wt% |
| Chemical Composition (Ni) | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 | wt% |
| Chemical Composition (Mo) | — | 2.0–3.0 | — | wt% |
| Chemical Composition (Ti) | — | — | 5×C to 0.70 | wt% |
| Thermal Conductivity (20°C) | 16.3 | 16.3 | 15.1 | W/(m·K) |
| Thermal Conductivity (500°C) | 26.3 | 26.3 | 26.3 | W/(m·K) |
| Specific Heat (20°C) | 500 | 500 | 500 | J/(kg·K) |
| Linear Expansion Coefficient (20–100°C) | 17.3 | 17.0 | 17.8 | ×10⁻⁶/K |
| Tensile Strength (Annealed) | ≥515 | ≥450 | ≥515 | MPa |
| Yield Strength (Annealed) | ≥205 | ≥170 | ≥205 | MPa |
| Maximum Service Temperature | 870 | 870 | 980 | °C |
| Minimum Service Temperature | -196 | -196 | -196 | °C |
| Density (20°C) | 7.93 | 8.00 | 7.95 | g/cm³ |
2.3 Surface Finish Options
- Pickled & Passivated (2B Finish): Standard surface treatment providing a smooth, corrosion-resistant finish with Ra ≤ 0.5 μm
- Mechanical Polish: Mirror finish with Ra ≤ 0.1 μm for applications requiring minimal condensate adhesion
- Electro-polished: Ultra-smooth finish with Ra ≤ 0.05 μm, enhanced passive film integrity
- Chemical Passivation: ASTM A967 compliant passivation treatment for maximum passive layer formation
3. Technical Specifications
3.1 Dimensional Parameters
| Parameter | Specification Range | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 50.8 mm (1/8" – 2") | ASTM A213 / A269 |
| Wall Thickness | 0.25 mm – 3.00 mm | ASTM A213 / A269 |
| Coil Inner Diameter (CID) | 50 mm – 500 mm (2" – 20") | Custom / Application-specific |
| Coil Outer Diameter (COD) | 75 mm – 600 mm (3" – 24") | Custom / Application-specific |
| Coil Length (Straightened Equivalent) | 1.0 m – 30.0 m (per coil) | Custom / Application-specific |
| Number of Turns | 2 – 50 turns | Custom / Application-specific |
| Pitch (Turn-to-Turn Spacing) | 1.5 × OD – 3.0 × OD (minimum) | Engineering Design |
| Straight Leg Length (Inlet/Outlet) | 50 mm – 200 mm | Custom / Application-specific |
| End Connection Type | Flat, Beveled, Threaded (NPT/BSP), Flanged | ASME B1.20.1 / B16.5 |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade) / ±0.10 mm (standard) | ASTM A213 |
| Dimensional Tolerance (Wall) | ±10% of nominal | ASTM A213 |
| Roundness Tolerance | ≤ 2% of OD | ASTM A213 |
3.2 Performance Parameters (Vertical Film Condensation)
| Performance Parameter | Typical Value / Range | Notes |
|---|---|---|
| Heat Transfer Coefficient (ho) | 1,500 – 8,000 W/(m²·K) | Depends on fluid, velocity, geometry |
| Enhancement Factor vs. Straight Tube | 1.30 – 1.50 | Vertical spiral configuration |
| Maximum Operating Pressure | Up to 10.0 MPa (1450 psi) | Hydrostatic test at 1.5× working pressure |
| Pressure Drop per Coil | 0.01 – 0.50 bar (internal flow) | Depends on flow rate and geometry |
| Condensate Film Thickness | 0.1 – 0.5 mm (typical) | Natural convection condensation |
| Approach Temperature | 1.0 – 5.0 K | Depends on design and flow arrangement |
3.3 Applicable Standards & Specifications
- ASTM A213 / A213M — Seamless austenitic stainless steel boiler, heat-exchanger, and condenser tubes
- ASTM A269 / A269M — Seamless austenitic stainless steel tubing for chemical and heat-exchange equipment
- ASTM A312 / A312M — Seamless and welded austenitic stainless steel tubing for chemical and heat-exchange equipment
- ASME B31.3 — Process piping design code
- EN 10216-5 — European standard for austenitic stainless steel tubes
- JIS G3459 — Japanese Industrial Standard for seamless austenitic stainless steel tubes
- GB/T 13296 — Chinese national standard for seamless stainless steel tubes for heat exchangers
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection: Ingot or hot-rolled coil sourcing from certified mills with full chemical composition verification (spectroscopic analysis) and mechanical property certification (mill test reports).
- Tube Forming: Seamless tubes produced via hot-piercing and cold-drawing/rolling processes, or welded tubes produced via ERW (Electric Resistance Welding) with subsequent solution annealing. Tubes are cold-worked to achieve precise dimensional tolerances.
- Solution Annealing & Pickling: Tubes undergo solution heat treatment at 1010°C–1150°C followed by rapid water quenching to achieve full solution-annealed condition. Subsequent acid pickling removes oxide scale and prepares surface for passivation.
- Passivation: Chemical passivation treatment per ASTM A967 using nitric acid or citric acid solutions to establish a chromium-rich passive oxide layer on the surface.
- Spiral Coiling (Tube Bending): Precision CNC-controlled coil winding using mandrel-assisted bending technology. The bending process employs:
- Constant bending radius control to prevent ovality and wall thinning
- Internal mandrel support to maintain circular cross-section integrity
- Controlled bending speed to minimize residual stress and work hardening
- Post-bend stress relief annealing (optional) at 870°C–1050°C to restore full annealed properties
- End Forming & Connection Preparation: Tube ends are cut square (±0.5°), deburred, and formed to the specified connection type (beveled, threaded, or flanged).
- Quality Inspection & Testing: Comprehensive inspection including dimensional verification, visual examination, hydrostatic pressure testing, and optional eddy current testing for wall thickness and defect detection.
- Final Cleaning & Packaging: Tubes are cleaned with approved solvents, dried, and packaged with protective end caps and moisture-absorbing desiccants in export-grade wooden crates or steel containers.
4.2 Critical Manufacturing Parameters
| Process Step | Control Parameter | Tolerance / Requirement |
|---|---|---|
| Coil Bending | Minimum Bending Radius | ≥ 3 × OD (cold bending without mandrel) |
| Coil Bending | Wall Reduction at Bend Apex | ≤ 8% of nominal wall thickness |
| Coil Bending | Ovality at Bend | ≤ 3% of OD |
| Coil Bending | Springback Compensation | Pre-calculated based on material grade and geometry |
| Hydrostatic Test | Test Pressure | 1.5 × Maximum Working Pressure |
| Hydrostatic Test | Hold Time | ≥ 10 seconds per coil |
| Stress Relief | Annealing Temperature | 870°C – 1050°C (depending on grade) |
| Stress Relief | Cooling Method | Air cooling or furnace cooling |
5. Applications
5.1 Primary Application Domains
- Refr